The present invention relates generally to a brushless motor drive circuit formed as a semiconductor integrated circuit.
More particularly, the present invention relates a brushless motor drive circuit in which induced voltages generated across exciting coils of respective phases are detected and, for each of the exciting coils of respective phases, a rotor position signal is produced which is a square wave signal and whose half period corresponds to a period from a polarity inversion of the induced voltage to the next polarity inversion of the induced voltage. Based on the rotor position signals, switching elements are square wave on-controlled and/or pulse width converted square wave PWM (Pulse Width Modulation) controlled, and thereby excitation of the exciting coils is controlled.
FIG. 10 shows a circuit including a conventional semiconductor integrated circuit 100 for driving a brushless motor. As shown in FIG. 10, the semiconductor integrated circuit 100 is coupled with a star connection type three-phase brushless motor 1, a microcomputer 2 for supplying a rotation speed control signal of the motor 1, a DC power source VDD, and the ground. Exciting coils 3, 4 and 5 of the motor 1 are star-connected and correspond to U phase, V phase and W phase, respectively. One terminals of the exciting coils 3, 4 and 5 are coupled to a U phase terminal U, a V phase terminal V and a W phase terminal W, respectively, and the other terminals of the exciting coils 3, 4 and 5 are commonly coupled, as the midpoint, to a midpoint terminal C. The microcomputer 2 is coupled to an input terminal S.
The semiconductor integrated circuit 100 comprises a bridge output circuit 6 which supplies excitation currents for respective phases to the exciting coils 3, 4 and 5 in predetermined timing. The current value of each of the excitation currents is controlled by PWM control. The semiconductor integrated circuit 100 also comprises a detector circuit 7 which senses induced voltages generated across the exciting coils 3, 4 and 5, and produces square wave rotor position signals PU, PV and PW. A half period, that is, xcfx80 radian, of each of the rotor position signals PU, PV and PW corresponds to a period from a zero-cross in which a polarity of an induced voltage inverts to the next zero-cross in which the polarity of the induced voltage inverts next time. The semiconductor integrated circuit 100 further comprises an inner voltage generating circuit 8 for generating an inner voltage as a voltage for pulse width modulation which varies according to a voltage of the rotation speed control signal supplied from the microcomputer 2. The semiconductor integrated circuit 100 also comprises a triangular wave generating circuit 9 for generating a triangular wave voltage, and a comparator 10 for generating a PWM signal obtained by pulse width modulating the inner voltage from the inner voltage generating circuit 8 by using the triangle wave voltage from the triangle wave generating circuit 9. The semiconductor integrated circuit 100 further comprises a control circuit 11 which performs excitation or current conduction timing control and PWM control for the bridge output circuit 6, based on the PWM signal from the comparator 10 and the rotor position signal from the detector circuit 7.
The bridge output circuit 6 comprises P-channel type MOS transistors Q1, Q2 and Q3 which control current conduction timing into the exciting coils 3, 4 and 5, respectively, and N-channel type MOS transistors Q4, Q5 and Q6 which perform PWM control of current values to the exciting coils 3, 4 and 5 in predetermined timing. The control circuit 11 supplies current conduction timing control signals to the gate electrodes of the MOS transistors Q1, Q2 and Q3, and supplies current quantity control signals to the MOS transistors Q4, Q5 and Q6. The main current paths of the MOS transistors Q1 and Q4, the MOS transistors Q2 and Q5, and the MOS transistors Q3 and Q6 are respectively coupled in series. The source electrodes of the MOS transistors Q1, Q2 and Q3 are commonly coupled to the power source VDD and the source electrodes of the MOS transistors Q4, Q5 and Q6 are commonly coupled to the ground. The common connection node between the MOS transistors Q1 and Q4, the common connection node between the MOS transistors Q2 and Q5 and the common connection node between the MOS transistors Q3 and Q6 are coupled with the terminals U, V and W of the motor 1, respectively.
The detector circuit 7 detects or senses the induced voltages generated across the exciting coils 3, 4 and 5 via the terminals U, V, W and C. By using integrating circuits and comparators which are provided within the detector circuit 7 and which are not shown in the drawing, the detector circuit 7 produces the square wave rotor position signals PU, PV and PW. A half period, that is, xcfx80 radian, of each of the rotor position signals PU, PV and PW corresponds to a period from a zero-cross in which a polarity of an induced voltage inverts to the next zero-cross in which the polarity of the induced voltage inverts again next time.
The control circuit 11 receives the PWM signal from the comparator 10 and the rotor position signals PU, PV and PW from the detector circuit 7. Thereby, the control circuit 11 determines current conduction timing to the respective exciting coils 3, 4 and 5. The control circuit 11 produces the current conduction timing control signals supplied to the gate electrodes of the MOS transistors Q1, Q2 and Q3 and the current quantity control signals supplied to the gate electrodes of the MOS transistors Q4, Q5 and Q6. At a start time of the motor, the induced voltages are not generated across the exciting coils 3, 4 and 5, so that the detector circuit 7 does not produce the rotor position signals PU, PV and PW. Therefore, at a start time of the motor, predetermined start pattern signals are supplied to the control circuit 11 from a start circuit not shown in the drawing.
With reference to FIG. 10 and FIGS. 11A-11D, an explanation will be made on an operation of the semiconductor integrated circuit 100 which has the above-mentioned structure, when the semiconductor integrated circuit 100 is coupled with the motor 1 as shown in FIG. 10. A detailed explanation on the control of current conduction timing and current quantities of the respective exciting coils 3, 4 and 5 will be provided later. The control circuit 11 sets the current conduction timing as shown in FIG. 11A. As shown in FIG. 11D, the control circuit 11 supplies the current conduction timing control signals of square waves to the gate electrodes of the MOS transistors Q1, Q2 and Q3, and supplies the current quantity control signals to the gate electrodes of the MOS transistors Q4, Q5 and Q6 at respective timing. Each of the current quantity control signals is a pulse width converted square wave PWM signal and has a constant on-duty cycle during each control timing. The on-duty cycle of the pulse width converted square wave PWM signal varies depending on the required current quantity. In order shown in FIG. 11B, the MOS transistors Q1, Q2 and Q3 are on-controlled by square wave signals (SQ-ON CONTROL), and also the MOS transistors Q4, Q5 and Q6 are pulse width converted square wave PWM controlled (PWSQ-PWM CONTROL). In the motor 1, among the exciting coils 3, 4 and 5 of three phases, a current flows from the exciting coil of the phase coupled to a high side voltage, i.e., VDD, to the exciting coil of the phase coupled to a low side voltage, i.e., the ground, in order shown in FIG. 11A. That is, the exciting coils of two phases are sequentially energized in order of phase shown in FIG. 11A and thereby the rotor of the motor 1 rotates. The direction of the current varies such that the following 6 conditions are sequentially repeated. That is, a condition a current flows from the terminal U to the terminal V, a condition a current flows from the terminal U to the terminal W, a condition a current flows from the terminal V to the terminal W, a condition a current flows from the terminal V to the terminal U, a condition a current flows from the terminal W to the terminal U, and a condition a current flows from the terminal W to the terminal V.
The current conduction or energizing timing of the respective exciting coils 3, 4 and 5 of the motor 1 is controlled as follows. The induced voltages generated across the respective exciting coils 3, 4 and 5 are supplied to the detector circuit 7 via the terminals U, V, W and C. By using the integrating circuits and the comparators which are provided inside the detector circuit 7 and which are not shown in the drawing, the detector circuit 7 produces the rotor position signals PU, PV and PW having waveforms shown in FIG. 11C and supplies these signals to the control circuit 11. After receiving the rotor position signals PU, PV and PW, the control circuit 11 determines the current conduction timing based on the rotor position signals PU, PV and PW, and supplies the gate voltage signals as shown in FIG. 11D to the MOS transistors Q1, Q2 and Q3 and to the MOS transistors Q4, Q5 and Q6. Thereby, the MOS transistors Q1, Q2 and Q3 are square wave on-controlled and the MOS transistors Q4, Q5 and Q6 are pulse width converted square wave PWM controlled, in accordance with the timing shown in FIG. 11B.
On the other hand, quantity of current supplied to the exciting coils 3, 4 and 5 of the motor 1 is controlled as follows. That is, when the rotation speed control signal is supplied to the inner voltage generating circuit 8 from the microcomputer 2, the inner voltage generating circuit 8 converts the rotation speed control signal into an inner voltage signal which is supplied to the non-inverting (+) input terminal of the comparator 8. The comparator 8 compares the inner voltage signal with a triangular wave signal from the triangular wave generating circuit 9 and generates a PWM signal supplied to the control circuit 11. The PWM signal is used for controlling a motor current such that a desired rotation speed is obtained. By using the PWM signal and based on the current conduction timing determined as mentioned above, the current quantity control signals are generated which are used for performing the pulse width converted square wave PWM control according to the timing shown in FIG. 11B. The current quantity control signals are supplied to the gate electrodes of the MOS transistors Q4, Q5 and Q6 as shown in FIG. 11D. In combination with the square wave on-control of the MOS transistors Q1, Q2 and Q3 whose timing is shown in FIG. 11B, the direction of current flowing through the exciting coils varies such that the above-mentioned 6 conditions are sequentially repeated and, thereby, the motor 1 rotates. The rotation speed control signal supplied from the microcomputer 2 is produced as follows. That is, in an internal circuit not shown in the drawing, a rotation speed signal is generated from the rotor position signals PU, PV and PW obtained by the detector circuit 7, and supplied to the microcomputer 2. The microcomputer 2 compares the rotation speed signal with a signal corresponding to a desired rotation speed, and generates the rotation speed control signal from the difference voltage therebetween.
In this way, the MOS transistors Q1, Q2 and Q3 are square wave on-controlled and the MOS transistors Q4, Q5 and Q6 are pulse width converted square wave PWM controlled, and thereby rotation of the motor 1 is controlled.
In the above-mentioned semiconductor integrated circuit 100, the gate voltage waveforms of the MOS transistors Q1, Q2 and Q3, that is, the current conduction timing control signals, are on-controlled by using square wave signals. Also, the gate voltage waveforms of the MOS transistors Q4, Q5 and Q6, that is, the current quantity control signals, are PWM controlled for respective control timings by using pulse width converted square wave PWM waveforms each having a constant on-duty cycle. However, since the gate voltage waveforms are square waves, the motor 1 generates much noise at rising edge portions and falling edge portions of these waveforms.
A motor drive apparatus for solving such problem is proposed, for example, in Japanese patent laid-open publication No. 11-235079. In the motor drive apparatus disclosed in this publication, current signals supplied to motor exciting coils are soft switching controlled such that rising edges and falling edges of the current signals are sloped. In order to perform such soft switching control, in the motor drive apparatus disclosed in this publication, phase switching trapezoidal wave signals which are pulse signals obtained by sloping rising and falling edges of current conducting position signals, and composite trapezoidal wave signals are produced. The slope of the phase switching trapezoidal wave signals and composite trapezoidal wave signals is produced as follows. That is, pulses Tg are produced in response to the triggers by the rising and falling edges of the respective current conducting position signals, and pulses Vslope are produced in response to the triggers by the pulses Tg. Based on the pulses Vslope, the above-mentioned slope is produced, and therefore the slope is constant regardless of the rotation speed of the motor. Also, the rising and falling edges of the current conducting position signals are utilized as the rising and falling edges of the phase switching trapezoidal wave signals and composite trapezoidal wave signals as they are.
In the motor drive apparatus disclosed in the above-mentioned publication, current signals supplied to motor exciting coils are soft switching controlled such that rising edges and falling edges of the current signals are sloped. Therefore, magnetic flux of the rotor varies according to a sine function, and therefore deviation occurs between exciting magnetic flux of the motor exciting coils and magnetic flux of the rotor, so that effect of reducing noise becomes low. Therefore, in the motor drive apparatus disclosed in the above-mentioned publication, countermeasures against noise were insufficient.
Also, in order to perform the above-mentioned soft switching control, phase switching trapezoidal wave signals and composite trapezoidal wave signals are produced which are pulse signals obtained by sloping rising and falling edges of the current conducting position signals. The slope of the phase switching trapezoidal wave signals and composite trapezoidal wave signals is produced by first generating the pulses Tg in response to the triggers by the rising and falling edges of the respective current conducting position signals, and then by producing the pulses Vslope in response to the triggers by the pulses Tg. Based on the pulses Vslope, the above-mentioned slope is produced, and therefore the slope is constant regardless of the rotation speed of the motor. Therefore, when the rotation speed is low, the ratio of widths of the rising and falling edges of the current conducting position signals to a period of each of the current conducting position signals becomes small. Therefore, effect of reducing noise becomes low, and countermeasures against noise become insufficient.
Also, the rising and falling edges of the current conducting position signals are utilized as the rising and falling edges of the phase switching trapezoidal wave signals and composite trapezoidal wave signals as they are. Therefore, current conduction or energizing of the exciting coils is not performed in the optimum condition with respect to the position of the rotor, and it was impossible to obtain high rotation efficiency.
Therefore, it is an object of the present invention to provide a drive circuit for a brushless motor which can reduce noise of the brushless motor.
It is another object of the present invention to provide a drive circuit for a brushless motor which can reduce noise of the brushless motor even in a low rotation speed.
It is still another object of the present invention to provide a drive circuit for a brushless motor which can provide high rotation efficiency and which can reduce noise of the brushless motor.
It is still another object of the present invention to provide a drive circuit for a brushless motor which has relatively simple circuit structure and which can reduce noise of the brushless motor.
It is still another object of the present invention to obviate the disadvantages of the conventional drive circuit for a brushless motor.
According to an aspect of the present invention, there is provided a brushless motor drive circuit for driving a brushless motor which has a rotor and exciting coils of respective phases, the brushless motor drive circuit comprising: a detector circuit which detects an induced voltage generated across the exciting coil of each phase; a rotor position signal generating circuit which produces a square wave rotor position signal for the exciting coil of each phase, a half period of the rotor position signal corresponding to a time period from a polarity inversion of the induced voltage to the next polarity inversion of the induced voltage; a control circuit which, based on the rotor position signal, performs excitation control of the exciting coils by controlling switching elements for conducting excitation currents via the exciting coils, by using square wave on-control and/or pulse width converted square wave pulse width modulation (PM) control; and a pulse width converted sinusoidal wave PWM signal generating circuit which generates a pulse width converted sinusoidal wave PWM signal whose pulse width varies according to a sinusoidal function; wherein excitation of the exciting coils is controlled based on the pulse width converted sinusoidal wave PWM signal immediately before and after the square wave on-controlled portion and/or the pulse width converted square wave PWM controlled portion.
In this case, it is preferable that the exciting coils comprise three phase exciting coils, the excitation control comprises sequential excitation of exciting coils every two phases, and the switching elements comprises switching elements for controlling current conduction timing and switching elements for controlling current quantity, and wherein the switching elements for controlling current conduction timing are square wave on-controlled and the switching elements for controlling current quantity are pulse width converted square wave PWM controlled.
According to another aspect of the present invention, there is provided a brushless motor drive circuit for driving a brushless motor which has a rotor and exciting coils of three phases, the brushless motor drive circuit comprising: a detector circuit which detects an induced voltage generated across the exciting coil of each phase; a rotor position signal generating circuit which produces a square wave rotor position signal for the exciting coil of each phase, a half period of the rotor position signal corresponding to a time period from a polarity inversion of the induced voltage to the next polarity inversion of the induced voltage; a control circuit which, based on the rotor position signal, performs excitation control of the exciting coils by controlling switching elements for current conduction timing control and switching elements for current quantity control, the excitation control being performed by sequentially exciting the exciting coils of every two phases, the switching elements for current conduction timing control being square wave on-controlled and the switching elements for current quantity control being pulse width converted square wave PWM controlled; and a pulse width converted sinusoidal wave PWM signal generating circuit which generates a pulse width converted sinusoidal wave PWM signal whose pulse width varies according to a sinusoidal function; wherein excitation of the exciting coils is controlled based on the pulse width converted sinusoidal wave PWM signal immediately before and after the square wave on-controlled portion and/or the pulse width converted square wave PWM controlled portion.
It is preferable that a length of a half period of each of the rotor position signals of respective phases is counted to obtain a count value of T, wherein, from the count value of T, a value of T/2 is obtained by an operation, wherein a T/2 elapsed point in time is obtained which point is after T/2 from each edge immediately after the end of count of a half period of a rotor position signal of a phase in which the half period is counted, wherein the T/2 elapsed point in time is determined to be a switching point between the square wave on-control timings of two phases different from the phase in which the half period is counted or to be a switching point between the pulse width converted square wave PWM control timings of two phases different from the phase in which the half period is counted.
It is also preferable that the timing width of each of the square wave on-control portion and the pulse width converted square wave PWM control portion is 2T/3.
It is further preferable that the timing width of the pulse width converted sinusoidal wave PWM control portion is smaller than T/6.
It is advantageous that the timing width of the pulse width converted sinusoidal wave PWM control portion is determined based on the value T.
It is also advantageous that the timing width of the pulse width converted sinusoidal wave PWM control portion is a value obtained by dividing T by a multiple of 2.
It is further advantageous that the timing width of the pulse width converted sinusoidal wave PWM control portion is T/8.
It is preferable that, after obtaining T/2, T/4 and T/8 by an operation from T and obtaining (T/4+T/8) and (T/2+T/8) by an operation, a time period having a width of T/8 from a T/2 elapsed time to a (T/2+T/8) elapsed time from an edge immediately after the count end of the rotor position signal, and a time period having a width of T/8 from a (T/4+T/8) elapsed time to a T/2 elapsed time are determined to be the timing widths of the pulse width converted sinusoidal wave PWM control portions for other two phases different from the phase in which the rotor position signal is counted.
It is also preferable that, after obtaining T/64 by an operation from T and producing 8 shift signal which are sequentially shifted by T/64 in the timing width T/8 of the pulse width converted sinusoidal wave PWM control, a step voltage is obtained by dividing a voltage for pulse width modulation into 8 divided voltages by using voltage dividing ratios determined based on a sinusoidal function and by sequentially selecting a divided voltage from the 8 divided voltages by using the shift signals, and the pulse width converted sinusoidal wave PWM signal is obtained by pulse width modulating the step voltage by using a triangular wave voltage.
It is further preferable that the voltage for pulse width modulation, which is used for producing the pulse width converted sinusoidal wave PWM signals for performing the pulse width converted sinusoidal wave PWM control before and after the pulse width converted square wave PWM control, is also used for producing the pulse width converted square wave PWM signals for performing the pulse width converted square wave PWM control and is a voltage for performing pulse width modulation which varies depending on the rotation speed control signal, and wherein the voltage for pulse width modulation, which is used for producing the pulse width converted sinusoidal wave PWM signals for performing the pulse width converted sinusoidal wave PWM control before and after the square wave on-control, is the maximum value of a voltage for performing pulse width modulation which varies depending on the rotation speed control signal.
According to still another aspect of the present invention, there is provided a brushless motor drive circuit for driving a brushless motor which has a rotor and exciting coils of three phases, the brushless motor drive circuit comprising: a bridge output circuit which includes switching elements for current conduction timing control and switching elements for current quantity control and which performs excitation control by sequentially exciting the exciting coils every two phases; a detector circuit which detects an induced voltage generated across the exciting coil of each phase; a rotor position signal generating circuit which produces a square wave rotor position signal for the exciting coil of each phase, a half period of the rotor position signal corresponding to a time period from a polarity inversion of the induced voltage to the next polarity inversion of the induced voltage; a control circuit which, based on the rotor position signal, performs excitation control of the exciting coils by square wave on-controlling the switching elements for current conduction timing control and by pulse width converted square wave pulse width modulation (PWM) controlling the switching elements for current quantity control; a timing signal/shift signal generating circuit which generates timing signals and shift signals; and a pulse width converted sinusoidal wave PWM signal generating circuit which generates a pulse width converted sinusoidal wave PWM signal whose pulse width varies according to a sinusoidal function; wherein excitation of the exciting coils is controlled based on the pulse width converted sinusoidal wave PWM signal immediately before and after the square wave on-control portion and/or the pulse width converted square wave PWM control portion.
In this case, it is preferable that the timing signal/shift signal generating circuit comprises a T-counter which counts a length of a half period of each of the rotor position signals and outputs the count value obtained by this count as T, a hold circuit which holds the count value T, and an operation circuit which operates the count value T held by the hold circuit, the value T outputted from the T-counter and the rotor position signal to produce timing signals and shift signals.
It is also preferable that the operation circuit comprises: a T/2 operation circuit, a T/4 operation circuit, a T/8 operation circuit and a T/64 operation circuit which, based on the value T held in the hold circuit, produce T/2 signal, T/4 signal, T/8 signal and T/64 signal, respectively; a timing signal generating circuit which logically processes the T/2 signal, the T/4 signal, the T/8 signal, the T value from the T-counter and the rotor position signal to produce the timing signals; and a shift signal generating circuit which logically processes the T/64 signal and the timing signals to produce the shift signals.
It is further preferable that the timing signal generating circuit produces a first timing signal which has an edge at a point after elapsing T/2, a second timing signal which has an edge at a point after elapsing (T4+T/8), a third timing signal which has an edge at a point after elapsing (T/2+T/8), from an edge immediately after the count end of the rotor position signal.
It is advantageous that the control circuit produces the pulse width converted sinusoidal wave PWM control timing portions which include a timing portion having a width of T/8 from an edge of the first timing signal to an edge of the third timing signal obtained by an exclusive OR logical operation between the first timing signal and the third timing signal, and a timing portion having a width of T/8 from an edge of the second timing signal to an edge of the first timing signal obtained by an exclusive OR logical operation between the first timing signal and the second timing signal.
It is also advantageous that the pulse width converted sinusoidal wave PWM signal generating circuit comprises: a first step voltage generating circuit which receives the shift signals and the maximum value of a voltage for performing pulse width modulation that is used for producing the pulse width converted square wave PWM signals for performing the pulse width converted square wave PWM control and that varies depending on the rotation speed control signal, to produce a first step voltage; a second step voltage generating circuit which receives the shift signals and the voltage for performing pulse width modulation that varies depending on the rotation speed control signal, to produce a second step voltage; a first comparator which performs pulse width modulation of the first step voltage by using a triangular wave voltage and produces the pulse width converted sinusoidal wave PWM signals supplied to the switching elements for current conduction timing control; and a second comparator which performs pulse width modulation of the second step voltage by using a triangular wave voltage and produces the pulse width converted sinusoidal wave PWM signals supplied to the switching elements for current quantity control.